Recent increase of the calcium concentrations in Baltic Sea waters

The Baltic Sea is a large brackish water-system with an annual river input of 480 km3 or 2.2% of the Baltic Sea volume. Systematic studies on the chemical composition of Baltic Sea waters achieved some decades ago proved significant anomalies for most of the major constituents when compared with ionic ratios in ocean waters. We compare a present-day (1994/95) analysis of the calcium concentrations with our ‘historical’ data set from 1968–1970. The finding shows a mean Ca concentration increase of about 4% (compared to the analytical precision of ±0.08%) which corresponds to an increase of the overall average Ca flux via the freshwater from 3.1 to 4.5 g m−2 yr−1 within the past 25 years. The results suggest that this temporal change is man-induced and has an acidic character. The study shows that even the major chemical composition of large water bodies such as the Baltic Sea can be disturbed within a few decades when ‘global’ perturbations are effective in the drainage area.